High-altitude flight may be especially challenging for pilots due to the narrow range of acceptable airspeeds between the minimum and maximum operating airspeeds. An aircraft may easily be pushed out of this narrow range, and into a stall condition, by minor atmospheric disturbances (e.g., turbulence) or minor heading changes (or other adjustments) on the part of the pilot or crew. Most pilots are trained for low-altitude stall recovery but not for high-altitude stall recovery. For example, when the aircraft approaches an overspeed condition associated with a maximum operating speed (e.g., a maximum limit operating speed VMO given the particular airframe and the current altitude/atmospheric conditions) the aircraft will experience buffeting. Similarly, the aircraft will also experience buffeting when approaching an underspeed condition associated with a minimum operating speed (e.g., a VMIN or stall speed). At lower altitudes, the difference between buffeting associated with flying too fast and buffeting associated with flying too slow is clear to the pilot, who may then execute an appropriate response in each case.
At higher altitudes (e.g., approaching a “coffin corner” or aerodynamic ceiling) the separation between minimum and maximum operating speeds may be so small that the pilot may not clearly recognize whether the associated buffeting is a product of too little or too much airspeed. Consequently, the pilot's responsive action may be delayed (e.g., due to a preoccupation with manual flight control, which is far more difficult at higher altitudes, or a startled reaction to a sudden stall warning), inappropriate, or even counterproductive. For example, overcorrection for detected stall conditions (e.g., in or approaching an underspeed condition) may place the aircraft into an equally dangerous overspeed condition.
While autoflight and autopilot systems may provide more stable high-altitude flight control, these systems may not be used properly by pilots, or may not be programmed to effectively respond, in the event of a high-altitude stall or high-speed upset. Worse yet, the autopilot system may fail to quickly and effectively recover (being programmed for low-altitude rather than high-altitude response) and the pilot may compound the problem by disengaging the autopilot, manually attempting to recover from a high-altitude stall or high-speed upset with ineffective low-altitude recovery techniques.